I know I'm late to the game here with this, but I thought Bailey (Epicurus: The Extant Remains (1926)) had some interesting input for this discussion:
PD9 Εἰ κατεπυκνοῦτο πᾶσα ἡδονὴ, καὶ χρόνῳ καὶ περὶ ὅλον τὸ ἄθροισμα ὑπῆρχεν ἢ τὰ κυριώτατα μέρη τῆς φύσεως, οὐκ ἄν ποτε διέφερον ἀλλήλων αἱ ἡδοναί.
Bailey's translation:
If every pleasure could be intensified so that it lasted and influenced the whole organism or the most essential parts of our nature, pleasures would never differ from one another.
Bailey's is actually a little more literal some of the other translations.
Bailey translates ἄθροισμα as "organism," seeing this word as literally "the 'aggregate' of atoms of the sould and body which composes man." The word meant "things taken in the aggregate" in ancient Greek.
τὰ κυριώτατα μέρη > Bailey: "the most important parts', i.e., especially the mind rather than the body."
Bailey commentary:
"IX is a unique statement in Epicurus but very important, as it gives the ground for the differentiation of pleasures. Gassendi observed that it was directed against the Cyrenaics, who held (D L ii 87) that ‘no pleasure differs from any other nor is it more pleasant’: they believed also that pleasure was merely momentary and could not be prolonged, so that the object of life was to accumulate as many pleasurable moments as possible, and it did not matter from what source they were derived, life for them was simply and solely apolaustic [devoted to enjoyment]. Epicurus’ view, on the other hand, was that although pleasure could not be increased quantitatively beyond the limit of the complete absence of pain [PD3], yet pleasures could be varied, and had qualitative differences. Here he also implies that they can differ in ‘density’ in three ways, either by lasting longer or by affecting the whole organism or by affecting its more important parts (in particular, the mind). If all pleasures were alike in these respects, then there would be no difference at all between them, but as it is, a ‘calculus of pleasures ’ becomes possible, we can select our pleasures, either according as they are more pure, i e. more completely exclude pain (VIII and XI), or as they are more lasting or affect the whole organism or its more important parts. The theory is an integral part of the ethical scheme and is needed to complete the argument of Ep. iii, § 129."
Bailey goes on to connect PD9 with PD10 through PD13.
"X-XIII regarded as going together and are naturally approached from IX. Epicurus is applying the test of the κυριώτατα μέρη, and in particular of the mind. For its pleasure the necessary conditions are, as has been learnt from the Tetrapharmakos, a true knowledge of the nature of the gods and of death, and an understanding of the bounds to be set to desire and of the limits of pain. Now the pleasures of sensuality cannot help us here ; if they could, we might (apart fiom then accompanying pain) regard them as perfect pleasures. But for this purpose vie must turn rather to philosophy, which gives us the sure knowledge of the nature of the viorld and the principles of our own conduct. PD10 is a straightforward statement. If the pleasures of the body could give us what we need, we could find nothing to censure in them."